1. Field of the Invention
The invention relates to the use of antimisting additives for reducing the formation of aerosol in crosslinkable silicone coating compositions.
2. Description of the Related Art
A trend within the silicone coating industry is to increase machine speed in order to raise productivity. Where silicone coatings are applied to the substrate at relatively high speeds, of more than 300 m/min, for example, fine spray mists of the silicone coating system may be formed. This aerosol is formed at the silicone applicator unit. The formation of this spray mist proves to be a serious problem in the context of further increases in the coating speed.
The formation of this spray mist can be reduced by adding what are known as antimisting additives to the silicone coating system.
EP-A 716 115 (Dow Corning Corp.) describes antimisting additives obtained by reacting an organosilicon compound, a compound containing oxyalkylene groups, and a catalyst. The addition of these oxyalkylene-functional reaction products to crosslinkable silicone coating systems reduces the formation of aerosol in rapid coating processes.
WO 01/98418 (Dow Corning Corp.) discloses a liquid silicone antimisting composition, which is obtained by reacting    a) an organohydropolysiloxane having at least three Si—H groups (SiH) with    b) a compound having at least 2 alkenyl groups (C═C) in    c) the presence of a platinum catalyst and if desired    d) an inhibitorin a ratio of SiH/C═C≧4.6.
An extremely large excess of organohydropolysiloxane (SiH) is necessary in order to prevent gelling. This excess influences the release properties of the base system, the crosslinkable silicone coating composition. Furthermore, an inhibitor has to be added to prevent gelling.
U.S. Pat. No. 6,265,497 (Wacker-Chemie GmbH) describes siloxane copolymers containing Si-bonded hydrogen atoms as an intermediate in the preparation of alkenyl-functional siloxane copolymers which are branched and whose organopolysiloxane blocks are linked by hydrocarbon bridges.
An object of the invention was to provide antimisting additives for silicone coating compositions which reduce the formation of aerosol in rapid coating processes, which are readily miscible with the silicone coating compositions, and which do not impair the silicone coating compositions. These and other objects are achieved by including in the coating composition antimisting additives prepared by reacting a compound having minimally three aliphatic double bonds with an organosiloxane having terminal Si-bonded hydrogen atoms, in the presence of a hydrosilylatin catalyst, and optionally equilibrating with further linear, branched, or cyclic organopolysiloxanes.